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llvm-project/llvm/test/Transforms/LoopUnroll/rebuild_lcssa.ll

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Don't recompute LCSSA after loop-unrolling when possible. Summary: Currently we always recompute LCSSA for outer loops after unrolling an inner loop. That leads to compile time problem when we have big loop nests, and we can solve it by avoiding unnecessary work. For instance, if w eonly do partial unrolling, we don't break LCSSA, so we don't need to rebuild it. Also, if all exits from the inner loop are inside the enclosing loop, then complete unrolling won't break LCSSA either. I replaced unconditional LCSSA recomputation with conditional recomputation + unconditional assert and added several tests, which were failing when I experimented with it. Soon I plan to follow up with a similar patch for recalculation of dominators tree. Reviewers: hfinkel, dexonsmith, bogner, joker.eph, chandlerc Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D14526 llvm-svn: 253126
2015-11-14 13:51:41 +08:00
; RUN: opt < %s -loop-unroll -S | FileCheck %s
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
; This test shows how unrolling an inner loop could break LCSSA for an outer
; loop, and there is no cheap way to recover it.
;
; In this case the inner loop, L3, is being unrolled. It only runs one
; iteration, so unrolling basically means replacing
; br i1 true, label %exit, label %L3_header
; with
; br label %exit
;
; However, this change messes up the loops structure: for instance, block
; L3_body no longer belongs to L2. It becomes an exit block for L2, so LCSSA
; phis for definitions in L2 should now be placed there. In particular, we need
; to insert such a definition for %y1.
; CHECK-LABEL: @foo1
define void @foo1() {
entry:
br label %L1_header
L1_header:
br label %L2_header
L2_header:
%y1 = phi i64 [ undef, %L1_header ], [ %x.lcssa, %L2_latch ]
br label %L3_header
L3_header:
%y2 = phi i64 [ 0, %L3_latch ], [ %y1, %L2_header ]
%x = add i64 undef, -1
br i1 true, label %L2_latch, label %L3_body
L2_latch:
%x.lcssa = phi i64 [ %x, %L3_header ]
br label %L2_header
; CHECK: L3_body:
; CHECK-NEXT: %y1.lcssa = phi i64 [ %y1, %L3_header ]
L3_body:
store i64 %y1, i64* undef
br i1 false, label %L3_latch, label %L1_latch
L3_latch:
br i1 true, label %exit, label %L3_header
L1_latch:
%y.lcssa = phi i64 [ %y2, %L3_body ]
br label %L1_header
exit:
ret void
}
; Additional tests for some corner cases.
;
; CHECK-LABEL: @foo2
define void @foo2() {
entry:
br label %L1_header
L1_header:
br label %L2_header
L2_header:
%a = phi i64 [ undef, %L1_header ], [ %dec_us, %L3_header ]
br label %L3_header
L3_header:
%b = phi i64 [ 0, %L3_latch ], [ %a, %L2_header ]
%dec_us = add i64 undef, -1
br i1 true, label %L2_header, label %L3_break_to_L1
; CHECK: L3_break_to_L1:
; CHECK-NEXT: %a.lcssa = phi i64 [ %a, %L3_header ]
L3_break_to_L1:
br i1 false, label %L3_latch, label %L1_latch
L1_latch:
%b_lcssa = phi i64 [ %b, %L3_break_to_L1 ]
br label %L1_header
L3_latch:
br i1 true, label %Exit, label %L3_header
Exit:
ret void
}
; CHECK-LABEL: @foo3
define void @foo3() {
entry:
br label %L1_header
L1_header:
%a = phi i8* [ %b, %L1_latch ], [ null, %entry ]
br i1 undef, label %L2_header, label %L1_latch
L2_header:
br i1 undef, label %L2_latch, label %L1_latch
; CHECK: L2_latch:
; CHECK-NEXT: %a.lcssa = phi i8* [ %a, %L2_header ]
L2_latch:
br i1 true, label %L2_exit, label %L2_header
L1_latch:
%b = phi i8* [ undef, %L1_header ], [ null, %L2_header ]
br label %L1_header
L2_exit:
%a_lcssa1 = phi i8* [ %a, %L2_latch ]
br label %Exit
Exit:
%a_lcssa2 = phi i8* [ %a_lcssa1, %L2_exit ]
ret void
}
[LoopUnrolling] Fix a bug introduced in r259869 (PR26688). The issue was that we only required LCSSA rebuilding if the immediate parent-loop had values used outside of it. The fix is to enaable the same logic for all outer loops, not only immediate parent. llvm-svn: 261575
2016-02-23 05:21:45 +08:00
; PR26688
; CHECK-LABEL: @foo4
define i8 @foo4() {
entry:
br label %L1_header
L1_header:
%x = icmp eq i32 1, 0
br label %L2_header
L2_header:
br label %L3_header
L3_header:
br i1 true, label %L2_header, label %L3_exiting
L3_exiting:
br i1 true, label %L3_body, label %L1_latch
; CHECK: L3_body:
; CHECK-NEXT: %x.lcssa = phi i1
L3_body:
br i1 %x, label %L3_latch, label %L3_latch
L3_latch:
br i1 false, label %L3_header, label %exit
L1_latch:
br label %L1_header
exit:
ret i8 0
}
[LoopSimplify] When simplifying phis in loop-simplify, do it only if it preserves LCSSA form. llvm-svn: 282541
2016-09-28 05:03:45 +08:00
; CHECK-LABEL: @foo5
define void @foo5() {
entry:
br label %outer
outer:
br label %inner1
; CHECK: inner1:
; CHECK-NOT: br i1 true
; CHECK: br label %inner2_indirect_exit
inner1:
br i1 true, label %inner2_indirect_exit.preheader, label %inner1
inner2_indirect_exit.preheader:
br label %inner2_indirect_exit
inner2_indirect_exit:
%a = phi i32 [ %b, %inner2_latch ], [ undef, %inner2_indirect_exit.preheader ]
indirectbr i8* undef, [label %inner2_latch, label %inner3, label %outer_latch]
inner2_latch:
%b = load i32, i32* undef, align 8
br label %inner2_indirect_exit
inner3:
%a.lcssa = phi i32 [ %a.lcssa, %inner3 ], [ %a, %inner2_indirect_exit ]
br i1 true, label %outer_latch.loopexit, label %inner3
outer_latch.loopexit:
%a.lcssa.lcssa = phi i32 [ %a.lcssa, %inner3 ]
br label %outer_latch
outer_latch:
br label %outer
}